The present invention relates to a cooking control method for a food extruder, used at the time when producing direct-puffed snacks, using corn, rice and pulses as raw materials.
Conventional direct-puffed snacks are produced by using grits of corn, rice and pulses as raw materials, using a single screw extruder or twin screw extruder.
The quality of produced snacks is adjusted by controlling the degree of cooking by means of the extruder. Normally, the control of the cooking degree is performed in such a manner that measured values of a thermometer, a pressure gauge and an ammeter mounted on the extruder, number of revolutions and feed amount, etc., are checked, and a skilled operator personally performs sensory evaluation of products discharged from a nozzle, and takes the above measured values and the results of the sensory evaluation into consideration in order to properly adjust the extruder based on the operator""s experience.
However, the control of the cooking degree of the food extruder in the prior art depends mainly on the experience of the skilled operator, and the control procedure differs depending on the operator. Therefore, the quality of the product is not always constant.
Moreover, a great deal of experience and knowledge are required in order to become a skilled operator capable of producing excellent products, and it is difficult to control the extruder in a stable manner without being a skilled operator.
Furthermore, when a change in the material quality or a change of the material takes place, a long period of time is required for completing the adjustment of the extruder, and there is a disadvantage in that the productivity decreases during the adjustment period.
Also in the quality control, if the number of extruders controlled by one operator is increased, the quality control of the products produced by these extruders decreases, and therefore, there is a possibility that the difference in the quality of the products may increase.
On the other hand, an evaluation related to the quality of the produced puffed snack dough is performed by a sensory analysis. This sensory analysis is performed in such a manner that the quality of eating texture of the snack is divided into five stages, with point 5 being designated as the highest quality stage. If a product is evaluated as point 5 in the sensory analysis, then it is determined that there are no problems with the extruder. However, when a product is evaluated as less than a point 5, control of the extruder becomes necessary.
However, since it is not clear whether a cooking degree is too much or is not sufficient, by considering only the evaluation point, it is not possible to control the extruder based on the evaluation value alone.
The thermometer mounted on the food extruder is used for measuring the internal temperature of the machine itself, and not for measuring the temperature of the product. However, the internal temperature of the machine does not necessarily provide a close correlation with the product quality. Further, the relationship between the pressure and the product quality is not clear.
Therefore, it is an object of the present invention to provide a cooking control method for a food extruder, which can control cooking based on a measured value of a measuring instrument mounted on the extruder, and which can produce products having constant quality, without relying on the judgment of a skilled operator with respect to an operating state.
The cooking control method for the food extruder according to the present invention is characterized by performing control under computer management using fuzzy control in such a manner that a specific power consumption value is determined by dividing the electric energy consumed by a motor driving a rotational shaft of the food extruder in a unit time by the amount of dough material (hereinafter, also referred to as feed amount) supplied to the extruder in the unit time. The specific power consumption value at the time of producing snacks having excellent quality is designated as a reference value, and a control rule is established such that when a difference between the reference value of the specific power consumption value and the specific power consumption value is small, the number of revolutions of the food extruder is mainly controlled, and when the difference is large, the number of revolutions of the food extruder is controlled as well as the amount of water to be added, and the feed amount of the snack material.
The reference value of the specific power consumption value is a value with which a quality evaluation indicates as providing a snack having excellent quality. The reference value is set and controlled by a quality evaluation method wherein the quality evaluation of snacks is evaluated by physical measurements such as eating texture color tone and volume, thus differing from the conventional method. The eating texture is expressed by an eating texture evaluation value which is evaluated with a membership function value based on measured values of a bubble size of the snack and a cutting stress of the snack. The color tone is expressed by a color tone evaluation value which is evaluated with a membership function value based on a value measured using a spectrophotometric colorimeter. The volume is expressed by a volume evaluation value which is evaluated with a membership function value based on the weight of the snack stuffed in a container having a predetermined capacity. When there is even one defective evaluation value set in advance for each of the eating texture evaluation value, the color tone evaluation value and the volume evaluation value, the snack is estimated as having a defect in quality. When there is no defective evaluation value for each of the eating texture evaluation value, the color tone evaluation value and the volume evaluation value, each of the eating texture evaluation value, the color tone evaluation value and the volume evaluation value is multiplied by a weight coefficient distributed so as to approximate to the sensory evaluation value in the conventional method, so that the quality evaluation value can be obtained from the sum of the eating texture evaluation value, the color tone evaluation value and the volume evaluation value multiplied by the coefficients.
Moreover, the control method of an extruder according to the present invention is characterized in that upper limits, lower limits and adjusting values are determined for each of the number of revolutions, the feed amount of materials and the amount of water to be added, using as central values the specific power consumption value of the motor driving a rotational shaft of the extruder, the number of revolutions, the feed amount of materials and the amount of water added at the time of producing snacks having the most suitable quality evaluation value. The central value of the specific power consumption value is designated as a reference value, and the reference value of the specific power consumption value is compared with the specific power consumption value of the motor driving a rotational shaft of the extruder at the time of actual production of the snack. A result of the comparison is inputted into rules using a fuzzy theory, to thereby control each of the number of revolutions, the feed amount of snack materials and the amount of water to be added.
The rule based on the fuzzy theory is characterized in that each of an upper limit zone, a central zone, and a lower limit zone is set with each of the central values, serving as the reference values of the specific power consumption value, the upper limit and the lower limit, as the specific power consumption values. An adjusting value consisting of a predetermined value can be stepwise added to or subtracted from the number of revolutions within the range between the upper limit and the lower limit, in a manner as follows. When the specific power consumption value of the food extruder exists in the central zone formed of the reference value of the specific power consumption value, being the central value, adjusted with the positive/negative adjusting values, the number of revolutions, the feed amount of the materials and the amount of water added are maintained steady. When the specific power consumption value of the food extruder exists between the central zone and the upper limit, the number of revolutions is set to be the lower limit plus the adjusting value, and the feed amount of the materials and the amount of water added are set to be the central values. When the specific power consumption value of the food extruder exists between the central zone and the upper limit, and the number of revolutions is present at the lower limit plus the adjusting value, the number of revolutions is set to be the lower limit, and the feed amount of the materials and the amount of water added are set to be the central values. When the specific power consumption value of the food extruder exists between the central zone and the upper limit, and the number of revolutions is at the lower limit, the number of revolutions is set to be the lower limit, the feed amount of the materials is set to be the central value, and the amount of water added is set to be the upper limit. When the specific power consumption value of the food extruder exists between the central zone and the upper limit, the number of revolutions is at the lower limit and when the amount of water added is at the upper limit, the number of revolutions is set to be the lower limit, and the feed amount of the materials and the amount of water added are set to be the upper limits. When the specific power consumption value of the food extruder exists at the upper limit or above, the number of revolutions is set to be the lower limit, the feed amount of the materials is set to be the upper limit, and the amount of water added is set to be the upper limit. When the specific power consumption value of the food extruder exists between the central zone and the lower limit, the number of revolutions is set to be the upper limit minus the adjusting value, the feed amount of the materials is set to be the central value, and the amount of water added is set to be the central value. When the specific power consumption value of the food extruder exists between the central zone and when the lower limit, and the number of revolutions is at the upper limit minus the adjusting value, the number of revolutions is set to be the upper limit, the feed amount of the materials is set to be the central value, and the amount of water added is set to be the central value. When the specific power consumption value of the food extruder exists between the central zone and the lower limit and when the number of revolutions is at the lower limit, the number of revolutions is set to be the lower limit plus the adjusting value, the feed amount of the materials is set to be the central value, and the amount of water added is set to be the lower limit. When the specific power consumption value of the food extruder exists between the central zone and the lower limit and when the number of revolutions and the amount of water added are at the lower limits, the number of revolutions is set to be the upper limit minus the adjusting value, and the feed amount of the materials and the amount of water added are set to be the lower limits. When the specific power consumption value of the food extruder exists at the lower limit or below, the number of revolutions is set to be the upper limit, and the feed amount of the materials and the amount of water added are set to be the lower limits.
A cooking control system for a food extruder to be used in the present invention comprises feed means for adjusting the feed amount of the snack materials, hydration means for adjusting the amount of water to be added to the snack materials, processing means for heating and expanding the material dough obtained by mixing a predetermined amount of water in the snack materials with the food extruder to thereby produce the snacks, and control means for controlling the operating condition of each of the feed means, the hydration means and the processing means with a computer. A reference value of the specific power consumption value is obtained by dividing the electric energy consumed in a unit time by the drive motor which rotates the rotational shaft of the food extruder, at the time when the quality evaluations indicate the most suitable snack is obtained, by the amount of dough material supplied to the extruder in a unit time. The specific power consumption value is determined, per feed amount of the material actually supplied, from a ratio of the electric energy consumed at the time of actual production of snacks using the motor to the feed amount of the materials. The above-mentioned control means is controls the number of revolutions of the rotational shaft of the food extruder, when a relative difference between the reference value of the specific power consumption value and the specific power consumption value is small, and controls not only the number of revolutions but also an increase and decrease in the amount of water to be added, and an increase and decrease of the feed amount of the snack material, when the relative difference between the reference value of the specific power consumption value and the specific power consumption value is large.
The control means is characterized by determining each preferable value of the upper limit, the central value, the lower limit and the adjusting value for the specific power consumption value and the number of revolutions of the motor, the feed amount of materials and the amount of water added, based on the quality evaluation value of the most suitable snack, inputting the result of a comparison between the central value of the specific power consumption value and the actual power consumption of the motor, into the rule based on the fuzzy theory, and controlling each of the number of revolutions, the feed amount of snack materials and the amount of water added.
As a result, cooking control for the extruder, which has previously relied on skilled engineers, can be automated, thereby enabling stable production of the expanded snacks having an optimum quality.
The cooking control method for the food extruder according to the present invention will now be described, with reference to the drawings.